On Wednesday, the utility had to bring a third reactor at Browns Ferry Nuclear Plant down to 50 percent power to avoid environmental sanctions because the water in the Tennessee River - where the plant's cooling water is discharged - already was at 90 degrees.

Similar problems last summer forced the Tennessee Valley Authority to spent $50 million for replacement power, according to Golden. The extra expense translated to something between 50 cents and $1 on most electric bills several months later, officials have said.

To avoid similar heat problems this year, TVA in October began construction on a seventh cooling tower at Browns Ferry, which is near Athens, Ala., and officials expected the $80 million super tower to be complete in June or July.

But weather stormed that plan, too.

"It was delayed because of the impact of the tornadoes, and some spring storms and some heavy rains," Golden said. "It's probably about 98 percent complete, and we hope it will be in service in the next one to two months."

Both cooling towers at the Sequoyah Nuclear Plant in Soddy-Daisy were operational Wednesday as Chickamauga Lake temperatures approached the maximum allowed.

So far, the extreme heat has not had the same impact at Sequoyah or Watts Bar, both on Chickamauga Lake in Tennessee, but state environmental officials say TVA monitors river temperatures upstream and downstream of both plants and reports findings to the state.

If utility engineers see they can't bring the temperature to 86.9 degrees, they must slow or stop the plant's power production, said Tisha Calabrese-Benton, spokeswoman for the Tennessee Department of Environment and Conservation.

Fighting the heat

Chattanooga's July clocked in as fifth-hottest July on record, according National Weather Service meteorologist and intern Kate Guillet in Morristown, Tenn. In the Knoxvillle area, the month was the third-hottest July on record, and the Huntsville region near Browns Ferry recorded the 11th-warmest July. Weather Service records date back to 1850.

The rest of August is also going to be above normal in temperature, said Paul Barys, chief meteorologist for WRCB-TV Channel 3.

"Today [Wednesday] was 101. We smashed the record. The only thing that will cool us down are clouds right now," he said.

To help fight the heat, TVA uses the most recognizable structure of most nuclear plants -- the cooling towers.

Raw Tennessee River water is pumped into the nuclear plants and routed through pipes to absorb the heat from the plants' machinery. On cooler days, the water -- which never touches anything radioactive -- can be released directly back to the river as long as the returned water doesn't raise the downstream water temperature more than 5.4 degrees above the water temperature upstream of the plant.

But on the hottest of days, the water is routed through the cooling towers, where some of the heated water is released as steam, and the rest circulates until it is cool enough to be discharged to the river without harming temperature-sensitive fish and other aquatic life.

Browns Ferry, which began reducing power on Sunday, historically has had more difficulty meeting the cooling standard than any of TVA's other nuclear plants. That's because of differences in the plants and differences in the river and terrain near them, according to Golden and Calabrese-Benton.

"At Browns Ferry, the river is shallow and wide. The channels are deeper at Watts Bar and Sequoyah," Golden said. "Flow affects how warm the river gets."

Calabrese-Benton said the Tennessee plants have an advantage of more cold water feeding into the Tennessee River upstream of Sequoyah and Watts Bar from tributaries such as the Clinch and Hiwassee rivers.

Also Browns Ferry has three reactors, as opposed to the one operating at Watts Bar and two at Sequoyah.

The cooling towers, too, are different. The Tennessee plants have spool-like shapes and are tall. They use no electricity. But the Browns Ferry towers are only 50 feet tall but about 500 feet long. Each has 16 giant electric ceiling fans.

Golden said the new Browns Ferry cooling tower will be something of a "super" tower, compared to the existing six there now. It will be 1,000 feet in length and will have 28 mammoth fans.

"We think its cooling capacity will be enough to serve the entire plant without the other six," he said.

If that's not the case, TVA has planned to spend another $80 million refurbishing four of the other cooling towers, which are original to the 45-year-old Browns Ferry plant, he said.